The present invention relates to a dynamic RAM (Random Access Memory), a dynamic RAM module, and a method of refreshing them and, more particularly, to a refreshing technique for effective use mainly in RAM and RAM modules of large storage capacities.
A dynamic RAM holds information in an electrical charge form in capacitors, so that a refresh operation is required to prevent the stored information from being lost by reading the information from the memory, amplifying the read information, and restoring the information to its original storage state. Because information storage times of memory cells are not constant, a refreshing technique was proposed in Japanese Non-examined Patent Publication No. 61-217988 in which an address of a word line to be refreshed in a relatively short period is stored. In addition, a refreshing technique was proposed in Japanese Non-examined Patent Publication No. 51-127629 in which the addresses of all word lines are stored in the order in which the word lines are refreshed.